The present invention relates to agricultural implements and more particularly to a parking lock system for such implements. Such parking lock involves a positive brake system for securing the implement while parked, e.g. when the implement is uncoupled from the towing vehicle and left alone in the yard or on the field.
Many small agricultural implements are mounted on support wheels and are equipped with a towing bar for coupling the implement to a pulling vehicle such as a tractor. Because of the relatively small weight of the implement and the low maximum speed of the tractor, the road safety regulations do not always require to provide the implement with a wheel braking system which is coupled to braking system of the tractor and operated in conjunction therewith. The tractor has the necessary braking power to stop adequately both the tractor and the towed implement during road travel and field operations.
However when the implement is uncoupled and left to stand alone in the yard, on a public road or on the field, it may be necessary to provide extra means for securing the wheeled implement. It is well known in the art to use wedge blocks which can be installed in front of and/or behind one of the wheels to prevent the implement from running down a slope. It is also known to use a parking lock for securing one or both wheels to the frame of the implement. Commonly, the parking lock comprises a pin which can be inserted in a cavity of a circular member which is attached to the wheel or the wheel hub. Such apparatus is shown in GB 823.372. Herein a spring is provided for urging the pin into one of the cavities. For unlocking the wheel, a handle affixed to the pin is turned over along a ramp whereby the pin is lifted and pulled out of the cavity against the force of the spring. For locking the wheel the handle is turned in the other direction. The spring then forces the pin to the circular member and into one of the cavities.
It may happen that the border of the cavity is loaded so firmly against the pin, that a substantial force is needed to pull the pin out of the cavity. This occurs when the implement is parked on a slope or when the wheels got under stress by the maneuvers of the towing vehicle. If the pin cannot be pulled out manually, then it is a standard procedure to go back to the tractor, move the implement a little until the stress is off the wheel and then return to the implement for pulling out the pin. Such procedure is not very user-friendly and quite time-consuming.
Another known solution is to use a hydraulic or electrical actuator to remove the pin from the aperture. However such apparatus is relatively expensive, especially when compared to the full cost of the small implement it is used on.